Work will be concentrated primarily in the following areas: 1. Pathogenesis of immune thrombocytopenias; characterization of platelet auto- and iso- antigens. Methods of detecting iso-, auto-, and drug-dependent antibodies reactive with human platelets will be refined. Particular attention will be given to techniques involving 51Cr and 14C-serotonin release. The expression of HLA antigens on platelets and the genetic basis for its variation will be characterized. Platelet membrane antigens will be solubilized and purified and their reactivity with platelet antibodies of known specificity will be studied. Findings will be applied to study of the pathogenesis of the immune thrombocytopenic disorders and to the development of improved methods of platelet transfusion therapy. 2. Molecular Basis of the Platelet "Storage Lesion". Biochemical changes occurring in platelets upon being concentrated, resuspended, and stored under standard blood banking conditions will be further characterized. In the coming year, priority will be given to cyclic nucleotides and their synthetic systems and to glycogen metabolism. Findings will be applied to the development of improved methods of short-term platelet preservation. BIBLIOGRAPHIC REFERENCES: Casper JT, Varma RR, Lewis JD, Harrington GJ, Aster RH: Exchange transfusion in Reye's syndrome with saline-washed red blood cells. Transfusion 16:130, 1976. Aster RH, Becker GA, Filip DJ: Studies to improve methods of short-term platelet preservation. Transfusion 16:4, 1976.